Gram-positive bacterial pathogens inflict an enormous burden of human disease world-wide. This closely related group of microbes includes Bacillus anthracis, the most notorius bioterror agent, as well as Staphylococcus aureus, which, judged by human morbidity, is currently the single most important infectious agent in the United States. Broad dissemination of antibiotic (methicillin) resistant S. aureus (MRSA) strains in American communities implies the return of the pre-antibiotic era unless new therapies can reduce human mortality. B. anthracis has been weaponized and engineered to acquire antibiotic resistance traits that render currently available antibiotics ineffective and human populations defenseless, if they had been exposed to drug-resistant anthrax spores. The GLRCE Research Project 3 proposal addresses the need for new antibiotics by unraveling molecular mechanisms that lead to assembly of siderophores, proteins, capsules or teichoic acids in the cell wall envelope of B. anthracis and S. aureus. Biosynthesis of all four types of compounds is either essential for bacterial growth or absolutely required for the pathogenesis of infection. An interdisciplinary team of researchers at Argonne National Laboratory, the University of Michigan and the University of Chicago applies multiple different technological platforms to focus on these questions: bioinformatics, molecular genetics, biochemical purification and assay development, structure determination, organic chemistry and small molecule inhibition, as well as infectious disease modeling. Products of this research are the in depth molecular appreciation of envelope function and pathogenesis in B. anthracis and S. aureus and the identification of small molecule inhibitors that will be tested for their property of antiinfective or antibiotic therapies. The specific aims are: 1. Inhibition of capsular biosynthesis in Bacillus anthracis;2. Inhibition of lipoteichoic acid biosynthesis in Bacillus anthracis and MRSA;3. Inhibition of iron siderophore biosynthetic pathways in Bacillus anthracis and MRSA;4. Inhibition of protein assembly pathways in the envelope of Bacillus anthracis and MRSA;5. Inhibition of siderophore amide hydrolases in B. anthracis and MRSA.